ABSTRACT

Studies on effect of autoexhaust emissions on ambient air quality and their impact on plant species exposed at selected traffic intersections in Delhi have been reported. The traffic survey, conducted at thirteen intersections, suggested 5 groups based on traffic volume. The general levels of lead in ambient air at five different intersections were in the range of 185 ng/m3 to 324 ng/m3 while background concentration was 62 ng/m3. Lead content of soil in all the pots of three species at all locations increased in May, 1985 as compared to February, 1985 content. Lead accumulation in plant had significant variation between two seasons. The concept of Lead Pollution Tolerance Index has been proposed for determination of the suitability of a plant species for roadside plantation.

Key-Words: Autoexhaust; Lead Pollution; Roadside vegetation; Lead Pollution Tolerance Index; Ambient Air Quality and Impact Assessment

INTRODUCTION

Atmosphere, soil and vegetation in the roadside ecosystem contain elevated levels of lead originating from the combustion of leaded gasoline by motor vehicles. The road length of about two million Km and about ten million vehicles (which include six million two wheelers and three wheelers) in India1 deserve serious understanding of the distribution and localization of lead and other pollutants in the roadside ecosystem.

Many studies abroad have shown considerable degree of pollution of the roadside ecosystem 2,3,4 but little information is available on this topic in Indian conditions 5,6,7. The autoexhaust emissions from about one million vehicles in Delhi city are of a major concern today. The number of petrol driven vehicles is far greater than the diesel vehicles. In order to asses the extent of autoexhaust lead pollution and study its impact on the roadside vegetation in Delhi city. Central Pollution Control Board has taken up studies systematically over a period of time. The present Paper deals with the studies carried out from January, 1984 to June, 1985 covering: (1) Assessment of traffic volume; (ii) Ambient air quality monitoring; and (iii) Impact assessment of plant species exposed at selected traffic intersections in the City.

EXPERIMENTAL ARRANGEMENTS

Thirteen traffic intersections were selected for the purpose of preliminary screening. Traffic census and ambient air quality monitoring (AAQM) for lead, SO2, NO2 and SPM were conducted during January, 1984. To reconfirm pattern of traffic volume and AAQM, exercise was repeated for the 13 sites in June, 1984. After evaluation of the observations of January and June, 1984 (Table 1), the traffic density at thirteen intersections was categorised into 5 different classes, i.e., I, II, III, IV and V (Table 2). Five traffic intersections were selected representing one traffic intersection from each class. Care was also taken that the selected intersections are geographically dispersed in a balanced manner over the City. The Nursery of the National Physical Laboratory-(NPL), New Delhi, was taken as a site relatively free from any lead pollution so as to serve as the control or background station. Fig. 1 shows the location of the traffic intersections selected for the detailed study and also the ones where studies were done in January and June, 1984.

After final selection of the sites, AAQM for Pb, SO2, NO2 and SPM was carried out at these six sites once every month. Traffic census was conducted once more in September, 1984 (Table 3). Traffic density was found to be in conformity with the observation patterns of January and June, 1984. In November, 1984, four selected plant species, grown in iso-ecological condition in the Nursery, were installed at all the six sites chosen for exposure study. A secured enclosure was built at each site. The plant species were :

Cynodon dactylon (Grass)
Alstonia Scholaris (Alstonia)
Nerium indicum (Kaner)
Eugenia Jambolana (Jamun)

At the end of first quarter, Cynodon Sp. was found to be destroyed by rodents. The species had to be excluded from the Study. As planned, plant species exposed at the six sites were harvested once in every three months for their growth performance study (February, 1985 and May, 1985 respectively).

METHOD OF SAMPLING AND ANALYSIS

Traffic Survey: The traffic volume at each traffic intersection was done manually by counting the number of motor vehicles entering the intersection from all the sides between 09.00 a.m. to 12.00 noon and 04.00 p.m. to 07.00 p.m., to cover morning and evening peak traffic hours.

AUTOEXHAUST LEAD

Traffic Census was done at 13 traffic intersections in January and June, 1984 and at 5 traffic intersections in September, 1984. The traffic survey conducted at thirteen intersections, suggested 5 groups based on traffic volume. These groups are : (V) less than 15,000; (IV) 15,000 to 20,000; (II) 20,000 to 25,000; (III) 25,000 to 30,000; and (I) more than 30,000 (Table 2). One road intersections is taken as representative of each of the 5 groups: (i) Azadpur; (ii) Ashram; (iii) Red Fort; (iv) India Gate; and (v) Delhi Gate. A station was maintained at National Physical Laboratory (NPL) Nursery as background station.

Table 1 : TRAFFIC VOLUME* AND AMBIENT AIR QUALITY AT DIFFERENT TRAFFIC INTERSECTIONS**

Sr.No.	Traffic Intersections	Traffic Volume 9 am to 12.00 : 6 4 pm to 7 pm : hr	Ambient Air Quality (10-hr average)
			SO2	NO2	SPM	Pb
				ug/m3	ng/m3
1.	Raja Garden	18,925	57	88	1,196	385
2.	Dhaula Kuan	16,996	47	64	778	559
3.	R.K. Puram X'ing	18,803	42	40	520	395
4.	A.I.I.M.S.	29,532	51	45	450	450
5.	Moolchand	33,252	65	60	460	1,802
6.	Ashram	18,450	53	73	607	395
7.	India Gate	27,729	28	28	282	514
8.	Delhi Gate	32,240	74	85	691	571
9.	Yamuna Bazar	18,773	64	76	702	390
10.	Red Fort	23,135	74	92	1,112	670
11.	Zakira	15,347	136	85	1,624	481
12.	Moti Nagar	23,973	81	70	492	563
13.	Azadpur	14,663	67	76	788	603